In the practice of composite fiber manufacturing, the common method has been the utilization of a plurality of thin, narrow strips of material, embedded with a variety of chemical elements, applied in repetitive applications or “lay-ups” onto a fixed or moving surface. The strips of chemically embedded material are commonly referred to as “tows” and a collection of tows in a wider, multiple tow presentation may be referred to as “tape.” In either case, tow or tape applications in multiple layers and repeated lay-ups are cause for the build-up of material that, when processed through an autoclave under closely monitored and controlled atmospheric conditions, yield a solid “composite” material of substantial strength, yet light in weight.
Accordingly, composite fiber placement manufacturing relies upon a fiber placement delivery system, generally achieved through the combination of a positioning device, or “positioner,” and a composite fiber tape or tow application device, which may generally be described as a “fiber application device.” The portion that directly controls the placement of the fiber tape or tow may also be referred to as an fiber placement head.
The positioner moves or articulates the fiber placement head into a location based upon a three-dimensional model having arbitrary directions which require the fiber application device to have multiple degrees of orientation and positioning, relative to the tool, mold or rotatable mandrel (hereinafter generally referred to as “the tool”).
During the fiber tow lay-up, the fiber placement head compresses the composite tows against the tool.
Several problems exist in the current state of the art relating to fiber placement manufacturing apparatuses and methods.
A further issue in current fiber placement manufacturing apparatuses and methods is the way that tows are prepared for lay-up within the fiber placement device prior to being used by the fiber placement head. Typically, individual tows are stored on spools located in a climate controlled creel. A layer of backing sheet separates the layers of fiber as they are wound around the spool. As the fiber is dispensed from the spool, in some systems, the backing sheet is removed from the fiber.
Unfortunately, if there are changes in the path along which the fiber tows are dispensed from the spool to the fiber placement head, when the path becomes shorter, slack occurs in the length of dispensed fiber tows which can cause bow-tying. This may occur such as when the fiber placement head is moved closer or farther away from the creel. One method to avoid bow-tying is to rewind the fiber tows onto the spool. However, because the backing sheet has been removed, if too much rewind occurs, fiber tow will be rewound directly onto other fiber tow which can cause the two layers to stick together causing problems in the system.
For instance, in some instances, a creel may be in a generally fixed position relative to a tool such with the fiber placement head being moved to place tow in varying locations. Such a fiber redirect mechanism is illustrated in U.S. patent application Ser. No. 11/510,165 to Hoffmann, filed Aug. 25, 2006, published as U.S. 2007/0044919 on Mar. 1, 2007, and assigned to the assignee of the instant application, the teachings and disclosure of which are incorporated herein by reference thereto.
Hoffman includes a fiber redirect mechanism which allows for the fiber placement head to be pivoted through a significant pivot angle. This fiber redirect mechanism is necessary as the creel in that application is prevented from pivoting or rotating along with the fiber placement head about various polar axis therein. As such, in Hoffmann, when the fiber placement head pivots about various axis within the wrist mechanism thereof, the location of the compaction roller of the fiber placement head changes is orientation relative to the creel.
Further, to adjust vertically, the entire fiber placement head is moved vertically towards or away from the creel which creates a significant change in the length of the tow path for individual tows as they travel from the spools within the creel to the fiber placement head.
Another problem can result in twisting a fiber tow over two short of a length. The shorter a length of the two that is twisted promotes increased localized twisting which can also degrade the tow. As such, if tows must be twisted, it is desired to twist them over an extended length. However, the desired longer length must be weighted against the overall size of the device such that tows can be placed in small female cavities of various shaped tools.